<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>&&</title>
</head>
<body>
    <script>
        var x=0,y=undefined;
        var m=1,n='imooc'
        console.log((x&&y));
        console.log((m&&n));
    </script>
</body>
</html>